What's Included on the Hydric Soils Lists
“Hydric Soils of the United States” is a compilation of all map units with either a major or minor component that is at least in part hydric. This could include components that are soil series, components that are classified at categories higher than the series level in Soil Taxonomy, and miscellaneous land types. Because the list includes both major and minor (small) percentages for map units in some cases most of the map unit may not be hydric. Also, some components may have a range of characteristics that cross the hydric/non-hydric soil boundary and, therefore, only a portion of that component may in fact be hydric. The list is useful in identifying map units that may contain hydric soils. The National List is generated once per calendar year (usually in January or February) to satisfy legislated mandates.
The Natural Resources Conservation Service (NRCS) Hydric Soils Lists, available here, are by soil map unit component. Detailed and up-to-date hydric soil lists (e.g. by soil survey area map unit component) are maintained by the NRCS State Offices and local field offices and can be downloaded from the Web Soil Survey at http://websoilsurvey.nrcs.usda.gov/.
The state lists are subsets of the national hydric soils list by state. For more detailed state lists by mapunit, contact the appropriate NRCS State Office.
NRCS has developed local lists of map units that contain hydric soils for each county, parish or soil survey area in the United States. These local lists are available at the NRCS State Offices, local NRCS field office, and on the Web Soil Survey at http://websoilsurvey.nrcs.usda.gov/ and are the preferred lists for use in making preliminary wetland determinations. Information from Web Soil Survey is the most up-to-date information as well as the official soil survey information. Since the National List is only compiled once a year and Web Soil Survey may be updated on a more frequent basis, Web Soil Survey should be deferred to when there is a discrepancy.